Add 'WARNING' to output

Test suite: None
Test baseline: N/A
Test namelist changes: N/A
Test status: N/A

Fixes: None

User interface changes?: No

Code review: None

utils/python/CIME/SystemTests/system_tests_compare_two_clone.py

@@ -121,7 +121,7 @@ def __init__(self,
                 # which would be wrong.
                 shutil.rmtree(self._caseroot2)
                 self._activate_case1()
-                logger.warning("Test case setup failed. Case2 has been removed, "
+                logger.warning("WARNING: Test case setup failed. Case2 has been removed, "
                                "but the main case may be in an inconsistent state. "
                                "If you want to rerun this test, you should create "
                                "a new test rather than trying to rerun this one.")